The present invention relates to a ballpoint pen containing an aqueous ink composition. More specifically, it relates to a ballpoint pen containing an aqueous ink composition in which ink is directly filled into an ink reservoir tube to directly feed the ink to a ballpoint pen tip without using an ink absorber, an ink feed rod and an ink feed controller.
Ballpoint pens containing an aqueous ink composition can be generally classified into three different types. In a first type, a ballpoint pen includes ink which is absorbed by an ink absorber arranged in an ink reservoir tube. The ink is fed to a ballpoint pen top via an ink feed rod arranged between the ink reservoir and the ballpoint pen tip. In a second type, a ballpoint pen is directly filled with ink into the ink reservoir tube. The ink is fed to the ballpoint pen tip via an ink feed controller and an ink feed rod arranged between the ink reservoir tube and the ballpoint pen tip. In the third type, a ballpoint pen is directly filled with ink into the ink reservoir tube, and the ink is directly fed to the ballpoint pen tip without using the ink absorber, the ink feed rod and the ink feed controller.
The above-mentioned third type ballpoint pen has an advantage that a large amount of ink is reserved and all the ink can be used. However, in view of the structure of this ballpoint pen, it is necessary that when the ballpoint pen is left as it is, i.e., when it is not used, the ink must be in a highly viscous state so as to prevent ink leakage through the ballpoint pen tip. When the ballpoint pen is used, the ball of the ballpoint pen is rotated to give shearing force to the ink, so that the viscosity of the ink lowers, and so that the ink is allowed to flow through the ballpoint pen tip. In addition, there are also more severe performance requirements, such that dripping of ink must be prevented while the ballpoint pen tip is allowed to stand in a downward direction, even under extreme condition such as temperature and humidity change. Moreover, it is also required that the ink feed remain good without any starving and splitting of the ink on the written lines. Furthermore, the contrast of the written lines must be high and the written lines must be sharp for a long period of time.
In order to meet the above-mentioned requirements, various suggestions have been heretofore made, but any concept which can sufficiently meet these requirements has not been obtained so far.
For example, an ink for writing implements has been suggested in which a crosslinked acrylic acid resin is used to impart thixotropy to the ink (Japanese Laid-Open Patent Application No. 57-49678/1982). However, this ink has the drawback as in the case of the third type of ballpoint pen mentioned above, in that the ink cannot be prevented from dripping from the ballpoint pen tip when the ballpoint pen tip is allowed to stand downward.